Prohibiting Failure Indications for Secondary Cell Group Failure

ABSTRACT

A UE operating in a network that supports dual connectivity operation is configured to minimize the transmission of unnecessary UE failure indications. The UE detects secondary cell group (SCG) failure for the UE, in response to detecting one of a plurality of SCG failure-triggering events. The UE sends a UE failure indication message, in response to the detecting SCG failure, and refrains from sending further UE failure indication messages in response to SCG failure-triggering events, until the sending of further UE failure indication messages is reenabled. In some cases, the UE sets a state of the UE to a UE prohibit state to prohibit sending further UE failure indication messages while in the UE prohibit state. In other cases, the UE starts a prohibit timer to prohibit sending further UE failure indication messages during the prohibit timer.

TECHNICAL FIELD

The present invention generally relates to wireless communicationnetworks, and particularly relates to failure detection andnotification.

BACKGROUND

The 3rd Generation Partnership Project (3GPP) is specifying the EvolvedUniversal Terrestrial Radio Access Network (E-UTRAN) consisting of theLong Term Evolution (LTE) and System Architecture Evolution (SAE)concepts. The architecture of the LTE system is shown in FIG. 1.

LTE dual connectivity is a feature defined from the user equipment (UE)perspective, where the UE may simultaneously receive data from andtransmit data to two different eNBs. This feature is part of 3GPPRel-12. The two different eNBs are usually denoted as Master eNodeB(MeNB) and Secondary eNodeB (SeNB). Operating on different frequencies,the MeNB and SeNB provide separate cell groups for the UE, a master cellgroup (MCG) and a secondary cell group (SCG).

The protocol architecture for Release 12 (Rel-12) of the 3GPPspecifications for LTE, as shown in FIG. 2, supports three types ofradio bearers: MeNB bearers, split bearers, and SeNB bearers. Inpre-Rel-12 LTE, i.e., before the introduction of dual connectivity,handover failures (HOF) and radio link failures (RLF) are detectable bythe UE. The UE tries to reestablish its connection upon detection ofsuch a failure. Otherwise, it goes to IDLE.

In detail, the following detection methods were considered. A handoverfailure timer, such as a T304 timer, is started upon reception of aradio resource control (RRC) connection reconfiguration message thatincludes mobility control information. The T304 timer is stopped uponsuccessful random access to a target handover cell. Expiration of theT304 timer triggers a procedure for reestablishment of the RRCconnection. A reestablishment timeout timer, such as a T311 timer, isstarted when the UE tries to reestablish RRC connection, and the T311timer is stopped when successfully reestablished. At expiration of theT311 timer, the UE goes to IDLE or declares that reestablishment isunsuccessful. A detection of physical-layer (PHY) failure timer, such asa T310 timer, is started when a physical layer problem is indicated byphysical layer, and the T310 timer is stopped when the physical-layerfailure is indicated as being resolved by the physical layer. Uponexpiration of the physical-layer failure timer, reestablishment of anRRC connection is triggered. The T310 timer can only be started ifreestablishment is not already ongoing (i.e., only if T311 is notrunning), and only after successful handover (i.e., only if T304 is notrunning).

Other failure detection methods include a random access procedure(random access channel or RACH) failure that triggers reestablishment ofan RRC connection if reestablishment is not already ongoing (T311 is notrunning), and only after successful handover (T304 is not running) Aradio link control (RLC) failure triggers reestablishment of an RRCconnection, if reestablishment not already ongoing (T311 is not running)RLC failure cannot happen when T304 is running, since a random accessprocedure is pending during that time period and RLC retransmissionshave not yet been started.

For dual connectivity, a new event, known as secondary-cell-groupfailure (SCG failure) or SeNB radio-link failure (S-RLF), has beenintroduced. When this event is triggered, the UE stops uplinktransmission in the SeNB, suspends SCG and split bearers, and sends anindication to the MeNB. The indication is sent via an RRC message inuplink and can be called a “UE failure indication,” which can beregarded as an “SCG Failure Information message.

The following are considered to be SCG failure-triggering events. An SCGchange failure timer (also known as a T307 timer), is started when SCGchange is triggered, and stopped after successful random access to a newSCG. The SCG change failure timer is similar to the pre-Rel-12 T304handover failure timer, but being related to the SCG, the proceduresimilar to handover is called SCG change. If the SCG change failuretimer expires, the UE triggers failure indication, with an RRC messageto the MeNB. An SCG physical layer (PHY) failure timer (also known as aT313 timer), is started when an SCG PHY problem is detected, but SCGchange is currently not ongoing (the SCG change failure timer is notrunning) The SCG PHY failure timer is similar to the pre-Rel-12 radiolink failure timer T310, but the SCG PHY failure timer is related to theSCG. This SCG PHY failure timer is stopped when an SCG physical layerproblem is indicated as being resolved by SCG PHY. If the SCG PHYfailure timer expires, the UE triggers failure indication in an RRCmessage to the MeNB. SCG MAC failure triggers the sending of a UEfailure indication in an RRC message to the MeNB, if SCG change is notcurrently ongoing (i.e., if the SCG change failure timer is not running)SCG MAC failure occurs when the UE has repeated random access proceduresand preamble transmissions more than a configurable threshold. SCG RLCfailure triggers the sending of a UE failure indication RRC message tothe MeNB, but SCG RLC failure cannot happen while the SCG change failuretimer is running SCG RLC failure occurs when the number of RLCretransmissions exceeds a configurable threshold.

In each of the failure events, it is assumed that the failure type isindicated in the RRC message. It is currently unclear how many UEfailure indication RRC messages are sent (and when) to the MeNB for theconcurrent SCG failure detection methods defined above. Too many UEfailure indications may waste radio resources and load the MeNBunnecessarily.

SUMMARY

Embodiments of the present inventive concepts describe the prohibitingof unnecessary UE failure indications from being sent upon SCG failuredetection. This can be achieved by a prohibit timer or a prohibit statein the UE.

According to some embodiments, a method, in a UE operating in a networkthat supports dual connectivity operation, for minimizing transmissionof unnecessary UE failure indications, includes detecting SCG failurefor the UE, in response to detecting one of a plurality of SCGfailure-triggering events. The method also includes sending a UE failureindication message, in response to the detecting SCG failure, andrefraining from sending further UE failure indication messages inresponse to SCG failure-triggering events, until the sending of furtherUE failure indication messages is reenabled.

In some cases, the refraining may include setting a state of the UE to aUE prohibit state to prohibit sending further UE failure indicationmessages while in the UE prohibit state. In other cases, the refrainingmay include starting a prohibit timer to prohibit sending further UEfailure indication messages during the prohibit timer.

According to some embodiments, a UE is adapted to detect SCG failure forthe UE, in response to detecting one of a plurality of SCGfailure-triggering events, send a UE failure indication message, inresponse to the detecting SCG failure, and refrain from sending furtherUE failure indication messages in response to SCG failure-triggeringevents, until the sending of further UE failure indication messages isreenabled.

In some cases, the UE is adapted to set a state of the UE to a UEprohibit state to prohibit sending further UE failure indicationmessages while in the UE prohibit state. In other cases, the UE isadapted to start a prohibit timer to prohibit sending further UE failureindication messages during the prohibit timer.

According to some embodiments, a method, in a network node, forminimizing transmission of unnecessary UE failure indications includesreceiving a UE failure indication message indicating that the UE isprohibited from sending UE failure indications in response to SCGfailure-triggering events, and sending an RRC connection reconfigurationmessage to indicate to the UE that the UE is reenabled to send UEfailure indications in response to SCG failure-triggering events.

According to some embodiments, a network node is adapted to receive a UEfailure indication message indicating that the UE is prohibited fromsending UE failure indications in response to SCG failure-triggeringevents, and send an RRC connection reconfiguration message to indicateto the UE that the UE is reenabled to send UE failure indications inresponse to SCG failure-triggering events.

Further embodiments may include computer program products andnon-transitory computer readable media that store instructions that,when executed by processing circuit, perform the operations of theembodiments describe above.

Of course, the present invention is not limited to the above featuresand advantages. Indeed, those skilled in the art will recognizeadditional features and advantages upon reading the following detaileddescription, and upon viewing the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example architecture of LTE.

FIG. 2 illustrates an architecture for 3GPP Rel-12, including supportfor three bearers.

FIG. 3 is a flowchart illustrating a method in a UE for minimizing thetransmission of unnecessary UE failure indications, according to someembodiments.

FIG. 4 is a flowchart illustrating another method in a UE for minimizingthe transmission of unnecessary UE failure indications, according tosome embodiments.

FIG. 5 is a block diagram of a UE configured to minimize thetransmission of unnecessary UE failure indications, according to someembodiments.

FIG. 6 is a flowchart illustrating a method in a UE for minimizing thetransmission of unnecessary UE failure indications, according to someembodiments.

FIG. 7 is a block diagram of a base station configured to provideinformation assisting a UE in minimizing the transmission of unnecessaryUE failure indications, according to some embodiments.

FIG. 8 is a flowchart illustrating a method in a base station forproviding information assisting a UE in minimizing the transmission ofunnecessary UE failure indications, according to some embodiments.

FIG. 9 is a block diagram of a functional implementation of a UE forminimizing the transmission of unnecessary UE failure indications,according to some embodiments.

FIG. 10 is a block diagram of a functional implementation of a basestation for providing information assisting a UE in minimizing thetransmission of unnecessary UE failure indications, according to someembodiments.

DETAILED DESCRIPTION

In LTE dual-connectivity scenarios, a UE failure indication upon SCGfailure may be transmitted multiple times. This is due to the fact thatthe evaluations of SCG PHY, SCG RACH and SCG RLC failure detection runin parallel, independently of each other. In LTE legacy behavior,concurrent SCG PHY, RACH, and RLC failure detection is handled byavoiding subsequent triggering of reestablishment if a T311 timer isrunning.

Embodiments described herein provide solutions to control multiple SCGfailure-triggering events in LTE dual connectivity.

Prohibit State

FIG. 3 illustrates use of a UE prohibit state to minimize unnecessary UEfailure indications. Once the UE triggers SCG failure (Block 302) andsends the UE failure indication message to the MeNB (Block 306), the UEconsiders itself in SCG failure state (Block 304). SCG failure state maybe triggered due to detection of an SCG change failure timer expiration,an SCG PHY failure timer expiration, an SCG RACH failure, or an SCG RLCfailure, for example. A UE state is set to a UE prohibit state (Block308). The prohibit state may be implemented by means of a UE variable.

During this UE prohibit state, the UE is not permitted to trigger SCGfailure, or send any more UE failure indications or corresponding RRCmessages in response to SCG failure-triggering events. For example, theUE is prohibited from starting an SCG PHY failure timer when it is inthe UE prohibit state. In another example, the UE is prohibited fromsending UE failure indications when the SCG PHY failure timer expires,if the UE is in the UE prohibit state. The UE is also prohibited fromsending UE failure indications when SCG RACH failure or SCG RLC failureis detected, when the UE is already in the UE prohibit state.

Upon the first successful RRC connection reconfiguration after settingthe UE prohibit state (Block 310), the UE state is reset (Block 312).This means that the UE prohibit state is toggled off so that the UE isagain allowed to send UE failure indications or to trigger SCG-failurestate. In some cases, the UE state is reset once the SCG change failuretimer is started. The UE state is reset when the UE goes from IDLE toCONNECTED, or when the UE is reconfigured to activate dual connectivity.

In some cases, the UE state is reset when the UE receives an RRCConnection Reconfiguration message reconfiguring SCG parameters, forexample, either releasing the SCG or modifying it. If the UE receives anRRC Connection Reconfiguration message that only configures MCGparameters, then the UE state is not impacted.

Prohibit Timer

FIG. 4 illustrates use of a UE prohibit timer to minimize unnecessary UEfailure indications. While in some scenarios it may be beneficial forthe MeNB to be informed multiple times about potentially different SCGfailures, it may be necessary to prohibit UE failure indications forsome time. When necessary, a UE failure indication is sent (Block 406)and the prohibit timer is started when SCG failure is triggered (Block402). SCG failure may be triggered upon detection of SCG change failureat the SCG change failure timer expiry, SCG failure due to the SCG PHYfailure timer expiry, SCG RACH failure or SCG RLC failure. The prohibittimer length may be configured by the network, including with RRCmessaging.

The prohibit timer will be started if the prohibit timer is not alreadyrunning (Block 404). During the duration of the prohibit timer, SCGfailure cannot be triggered and/or UE failure indications cannot be sentin response to SCG failure-triggering events. The prohibit timer canexpire (Block 408), which will again allow the sending of UE failureindications (Option 410) or the triggering of SCG failure (Option 412).

The timer may also be stopped upon the first successful RRC connectionreconfiguration after SCG failure was detected. In some cases, the SCGPHY failure timer is stopped once the SCG change failure timer isstarted. In some cases, the prohibit timer is stopped when the UEreceives RRC Connection Reconfiguration message reconfiguring SCGparameters, such as for either releasing the SCG or modifying it. If theUE receives an RRC Connection Reconfiguration that only configures MCGparameters, then the prohibit timer is not impacted.

Expiration of the prohibit timer may also indicate that the UE did notreceive an answer to the UE failure indication it tried to send. Forexample, the transmission failed, the MeNB did not send the answeringRRC connection reconfiguration, or the transmission of the MeNB answerfailed. In this case, the UE would be permitted to send another UEfailure indication due to SCG failure. This may indicate that theprohibition of UE failure indications has ended.

In a further embodiment, repeated transmission of the original UEfailure indication may be enforced upon expiration of the prohibittimer. In yet another embodiment, the latest reported failure type (SCGPHY, SCG MAC, SCG RACH, SCG RLC, or SCG change) should replace thefailure cause of the failure type of the original UE failure indication,and the UE failure indication should be sent again. Also, currentmeasurement results can be included in the new UE failure indication.

Some embodiments of the present inventive concepts are implemented by aUE 12 exemplified in FIG. 5. The UE 12 represents any wireless devicereferred to as a mobile terminal, wireless terminal and/or a mobilestation that may be portable, pocket-storable, hand-held,computer-comprised, or vehicle-mounted. For example, the UE 12 may be amobile telephone, cellular telephone, laptop, tablet computer, or surfplate with wireless capability. The UE 12 is enabled to communicatewirelessly with other devices, telephones or servers via a Radio AccessNetwork (RAN) and possibly one or more core networks, comprised within acellular communications network or wireless communication system,sometimes also referred to as a cellular radio system or a cellularnetwork. A cellular network covers a geographical area which is dividedinto cell areas, where each cell area is served by a radio network node.A cell is the geographical area where radio coverage is provided by theradio network node. The radio network node may be, for example, a basestation such as a Radio Base Station (RBS), eNB, eNodeB, NodeB, B node,or Base Transceiver Station (BTS), depending on the technology andterminology used. The base stations may be of different classes such asa macro eNodeB, home eNodeB or pico base station, based on transmissionpower and cell size.

Further, each radio network node may support one or severalcommunication technologies. The radio network nodes communicate over theair interface operating on radio frequencies with the wireless deviceswithin range of the radio network node. In the context of variousembodiments described herein, the expression downlink (DL) is used forthe transmission path from the base station to the wireless device. Theexpression uplink (UL) is used for the transmission path in the oppositedirection, such as from the wireless device to the base station.

As shown in FIG. 5, the UE 12 is arranged with radio circuitry 32 tocommunicate with radio network nodes, a memory 36 to store informationrelated to the embodiments, and a processing unit 30. The radiocircuitry 32 is configured to receive configuration messages, such as anRRC connection reconfiguration message, from a network node such as aneNB. The radio circuitry 32 is further configured to send a UE failureindication message. Memory 36 is configured to store information relatedto embodiments described herein and may include any mix of storagecircuits. The memory 36 may provide non-transitory storage for acomputer program and configuration data. The processing unit 30comprises appropriately configured processing circuitry, such as one ormore microprocessors, microcontrollers, digital signal processors,and/or other digital logic, and is configured to process data andinformation signaled to and from the radio circuitry 32.

According to some embodiments, the processing unit 30 is configured todetect SCG failure for the UE, in response to detecting one of aplurality of SCG failure-triggering events, and send a UE failureindication message, in response to the detecting SCG failure. Theprocessing unit 30 is also configured to refrain from sending further UEfailure indication messages in response to SCG failure-triggeringevents, until the sending of further UE failure indication messages isreenabled.

In some cases, the processing unit 30 is adapted to set a state of theUE to a UE prohibit state to prohibit sending further UE failureindication messages while in the UE prohibit state. In other cases, theprocessing unit 30 is adapted to start a prohibit timer to prohibitsending further UE failure indication messages during the prohibittimer. Optionally, the processing unit 30 is configured to reset the UEstate when a RRC connection reconfiguration message is received from abase station.

Regardless of its implementation details, the UE 12 in one or moreembodiments is configured to perform a method 600, operating in anetwork that supports dual connectivity operation, for minimizingtransmission of unnecessary UE failure indications, such as shown inFIG. 6. The method 600 includes detecting SCG failure for the UE, inresponse to detecting one of a plurality of SCG failure-triggeringevents (Block 610). These SCG failure-triggering events may include anexpiration of an SCG change failure timer, an expiration of an SCGphysical layer failure timer, an SCG RACH failure, an SCG MAC failure oran SCG RLC failure.

The method 600 also includes sending a UE failure indication message, inresponse to the detecting SCG failure (Block 620) and refraining fromsending further UE failure indication messages in response to SCGfailure-triggering events, until the sending of further UE failureindication messages is reenabled (Block 630).

In some cases, refraining from sending further UE failure messagescomprises setting a state of the UE to a UE prohibit state, whereinsending further UE failure indication messages is prohibited while inthe UE prohibit state (Block 640). An SCG PHY timer may also beprohibited from starting while in the UE prohibit state.

The UE state is reset in response to receiving an RRC connectionreconfiguration message, according to further embodiments. This mayinclude resetting the UE state in response to a RRC connectionreconfiguration message reconfiguring SCG parameters to release ormodify an SCG. The UE state can also be reset in response to areconfiguration message to activate dual connectivity, a start of an SCGchange failure timer, entering a connected state from an idle state, ordetermining that no answer to the UE failure indication was received.

In other cases, refraining from sending further UE failure messagescomprises starting a prohibit timer, where sending further UE failureindication messages is prohibited during the prohibit timer (Block 650).An SCG physical layer failure timer may be prohibited from startingwhile in the UE prohibit state. The length of the prohibit timer may beset according to a predetermined length or a length that is received ina message, such as an RRC message.

The prohibit timer may expire or be stopped under certain circumstances.For example, the prohibit timer is stopped in response to receiving anRRC connection reconfiguration message or a dual connectivityreconfiguration message from another communication device. The prohibittimer may also be stopped in response to the RRC connectionreconfiguration message reconfiguring SCG parameters to release ormodify an SCG. In some cases, the prohibit timer is stopped in responseto a first successful RRC configuration after SCG failure was detected.The prohibit timer may also be stopped in response to a start of an SCGchange failure timer, determining that no answer to the UE failureindication was received, entering a connected state from an idle state,or a reconfiguration to activate dual connectivity.

In further embodiments, the method 600 may include sending another UEfailure indication message upon expiration or stoppage of the prohibittimer. This may include resending the UE failure indication uponexpiration or stoppage of the prohibit timer. Sending another UE failureindication message may also include sending a latest reported failuretype instead of a failure type reported in the UE failure indication.Current measurement results may also be sent in the UE failureindication sent upon expiration or stoppage of the prohibit timer.

Some embodiments of the present invention are implemented by a radionetwork node, such as base station 10 exemplified in FIG. 7. The basestation 10 is arranged with radio circuitry 42 to communicate withserved wireless devices such as the UE 12, communication circuitry 48 tocommunicate with other radio network and core network nodes, memory 46to store information related to the embodiments, and a processing unit40. The communication circuitry 48 is configured to receive and sendfrom/to a core network node, such as a mobility management entity (MME),information and signaling related to embodiments described herein. Theradio circuitry 42 is configured to receive messages, such as a UEfailure indication message, from the UE 12 and send configurationmessages.

The memory 46 is configured to store information related to embodimentsdescribed herein and includes any mix of storage circuits. The memory 46may provide non-transitory storage for a computer program andconfiguration data. The processing unit 40 comprises appropriatelyconfigured processing circuitry, such as one or more microprocessors,microcontrollers, digital signal processors, and/or other digital logic,and is configured to process data and information signaled to and fromthe communication and radio circuitry 42, 48. The processing unit 40 isconfigured to receive a UE failure indication message indicating thatthe UE 12 is prohibited from sending UE failure indications in responseto SCG failure-triggering events, and send a RRC connectionreconfiguration message to indicate to the UE 12 that the UE 12 isreenabled to send UE failure indications in response to SCGfailure-triggering events.

Regardless of its implementation details, the base station 10 in one ormore embodiments is configured to perform a method 800, includingreceiving a UE failure indication message indicating that the UE 12 isprohibited from sending UE failure indications in response to SCGfailure-triggering events (Block 810), and sending a message, such as anRRC connection reconfiguration message, to indicate to the UE 12 thatthe UE 12 is reenabled to send UE failure indications in response to SCGfailure-triggering events (Block 820).

In some cases, the method 800 may include sending a length of a prohibittimer in an RRC message to the UE 12, wherein the prohibit timer of theUE 12 prohibits sending of UE failure indications during the prohibittimer.

It should be understood that the methods illustrated in FIGS. 3-4, 6 and8 are examples of the techniques described more fully above. Each ofthese methods may be modified according to any of the variations anddetails discussed. The methods illustrated in FIGS. 3-4, 6 and 8, andvariants thereof, may be implemented using the processing unitsillustrated in FIGS. 5 and 7, as appropriate, where the processing unitsare processing circuits configured with appropriate program code storedin memory circuits, to carry out the operations described above.Embodiments of the presently disclosed techniques further includecomputer program products for application in a wireless terminal as wellas corresponding computer program products for application in a basestation apparatus or other network node apparatus. The program code orcomputer program instructions may also be stored in a non-transitory andtangible computer-readable medium.

It will be further appreciated that various aspects of theabove-described embodiments can be understood as being carried out byfunctional “modules,” which may be program instructions executing on anappropriate processor circuits, hard-coded digital circuitry and/oranalog circuitry, or appropriate combinations thereof. For example, FIG.9 illustrates an example functional module or circuit architecture asmay be implemented in a UE 12, e.g., based on the processing unit 30 andthe memory 36, to operate the UE 12 in a network that supports dualconnectivity operation for minimizing transmission of unnecessary UEfailure indications. The illustrated embodiment at least functionallyincludes a detecting module 902 for detecting SCG failure for the UE 12,in response to detecting one of a plurality of SCG failure-triggeringevents. The implementation also includes a sending module 904 forsending a UE failure indication message, in response to the detectingSCG failure, and a refraining module 906 for refraining from sendingfurther UE failure indication messages in response to SCGfailure-triggering events, until the sending of further UE failureindication messages is reenabled.

In another example, FIG. 10 illustrates an example functional module orcircuit architecture as may be implemented in a base station 10, e.g.,based on the processing unit 40 and the memory 46, to operate the basestation 10 in a network that supports dual connectivity operation. Theillustrated embodiment at least functionally includes a receiving module1002 for receiving a UE failure indication message indicating that theUE 12 is prohibited from sending UE failure indications in response toSCG failure-triggering events, and a sending module 1004 for sending anRRC connection reconfiguration message to indicate to the UE 12 that theUE 12 is reenabled to send UE failure indications in response to SCGfailure-triggering events.

Thus, it is an object of embodiments herein to minimize unnecessary UEfailure indications upon SCG failure detection in a wirelesscommunication network. Advantages of the prohibit state and/or theprohibit timer of the embodiments include avoiding unexpected UEbehavior and/or unnecessary transmissions. By avoiding such waste ofradio resources, the system capacity will be increased.

Notably, modifications and other embodiments of the disclosedinvention(s) will come to mind to one skilled in the art having thebenefit of the teachings presented in the foregoing descriptions and theassociated drawings. Therefore, it is to be understood that theinvention(s) is/are not to be limited to the specific embodimentsdisclosed and that modifications and other embodiments are intended tobe included within the scope of this disclosure. Although specific termsmay be employed herein, they are used in a generic and descriptive senseonly and not for purposes of limitation.

What is claimed is:
 1. A method, in a user equipment (UE) operating in anetwork that supports dual connectivity operation, for minimizingtransmission of unnecessary UE failure indications, the methodcomprising: suspending secondary cell group (SCG) bearers, in responseto detecting a secondary cell-group failure (SCG-failure) triggeringevent; sending a UE failure indication message to the network;responsive to detecting the SCG-failure triggering event, entering aprohibit state in which the UE is not allowed to send further UE failureindication messages; and exiting the prohibit state in response to anyone of the following: transitioning from IDLE to CONNECTED state;receiving a reconfiguration message reconfiguring SCG parameters; andexpiry of a prohibit timer.
 2. The method of claim 1, wherein thedetected SCG-failure triggering event is one of: an expiration of an SCGchange failure timer; an SCG random access channel (RACH) failure; anSCG medium access control (MAC) failure; and an SCG radio link control(RLC) failure.
 3. The method of claim 1, wherein the method comprisesexiting the prohibit state in response to receiving a radio resourcecontrol (RRC) connection reconfiguration message reconfiguring SCGparameters to release or modify an SCG.
 4. The method of claim 1,wherein the method comprises exiting the prohibit state in response toreceiving a reconfiguration message to activate dual connectivity.
 5. Auser equipment (UE) comprising radio circuitry configured to communicatemessages within a wireless network and further comprising a processingcircuit configured to control the radio circuitry and to: suspendsecondary cell group (SCG) bearers, in response to detecting a secondarycell-group failure (SCG-failure) triggering event; send a UE failureindication message to the network; responsive to detecting theSCG-failure triggering event, enter a prohibit state in which the UE isnot allowed to send further UE failure indication messages; and exit theprohibit state in response to any one of the following: transitioningfrom IDLE to CONNECTED state; receiving a reconfiguration messagereconfiguring SCG parameters; and expiry of a prohibit timer.
 6. The UEof claim 5, wherein the detected SCG-failure triggering event is one of:an expiration of an SCG change failure timer; an SCG random accesschannel (RACH) failure; an SCG medium access control (MAC) failure; andan SCG radio link control (RLC) failure.
 7. The UE of claim 5, whereinthe processing circuit is configured to exit the prohibit state inresponse to receiving a radio resource control (RRC) connectionreconfiguration message reconfiguring SCG parameters to release ormodify an SCG.
 8. The UE of claim 5, wherein the processing circuit isconfigured to exit the prohibit state in response to receiving areconfiguration message to activate dual connectivity.
 9. Anon-transitory computer-readable medium comprising, stored thereupon,program instructions for a processing unit in a user equipment (UE),wherein the program instructions are configured so as to cause the UE,when the program instructions are executed by the processing unit, to:suspend secondary cell group (SCG) bearers, in response to detecting asecondary cell-group failure (SCG-failure) triggering event; send a UEfailure indication message to the network; responsive to detecting theSCG-failure triggering event, enter a prohibit state in which the UE isnot allowed to send further UE failure indication messages; and exit theprohibit state in response to any one of the following: transitioningfrom IDLE to CONNECTED state; receiving a reconfiguration messagereconfiguring SCG parameters; and expiry of a prohibit timer.